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GB/T 41119-2021 English PDF (GBT41119-2021)

GB/T 41119-2021 English PDF (GBT41119-2021)

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GB/T 41119-2021: Non-destructive testing -- Micromagnetic testing -- General principles

This document specifies the test method for stress, structural change, and phase transition of carbon steel and alloy steel materials by using the principle of micromagnetics. This document is applicable to the test of the stress distribution and its state, microstructure changes, and structural changes of carbon steel, alloy steel, and austenitic stainless steel; for the test of other metal materials, it can be used as a reference.
GB/T 41119-2021
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 19.100
CCS J 04
Non-destructive testing - Micromagnetic testing - General
principles
ISSUED ON: DECEMBER 31, 2021
IMPLEMENTED ON: JULY 1, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Method overview ... 5
5 Requirements for personnel ... 7
6 General testing technological procedures ... 7
7 Testing equipment and instruments ... 8
8 Testing ... 9
9 Evaluation of test results ... 11
10 Test records and report ... 12
Non-destructive testing - Micromagnetic testing - General
principles
1 Scope
This document specifies the test method for stress, structural change, and phase transition of carbon steel and alloy steel materials by using the principle of micromagnetics.
This document is applicable to the test of the stress distribution and its state, microstructure changes, and structural changes of carbon steel, alloy steel, and austenitic stainless steel; for the test of other metal materials, it can be used as a reference.
2 Normative references
The following documents contain the provisions which, through normative reference in this document, constitute the essential provisions of this document. For the dated referenced documents, only the versions with the indicated dates are applicable to this document; for the undated referenced documents, only the latest version (including all the amendments) is applicable to this document.
GB/T 12604.6 Non-destructive testing - Terminology - Eddy current testing GB/T 12604.10 Non-destructive testing - Terminology - Terms used in magnetic memory testing
GB/T 34357 Non-destructive testing - Terminology - Terms used in magnetic flux leakage testing
3 Terms and definitions
The terms and definitions defined in GB/T12604.6, GB/T12604.10 and GB/T34357 and the following terms and definitions apply to this document.
3.1 Micromagnetics
The magnetics that describes and studies the change of magnetic domain (the thickness of the domain wall and the range of single-domain particle size) during magnetization of ferromagnets at the mesoscopic scale.
3.2 Micromagnetic testing
A non-destructive testing method to obtain the stress distribution and its state, microstructure changes, and structural changes of materials through the micro-magnetic macro characterization of stress, phase transition, organization, structure and other features.
3.3 effective magnetic field
The vector sum of all magnetic fields acting on the magnetic moment.
3.4 Equivalent magnetic permeability
Under the action of an environmental magnetic field or external magnetic field, the local magnetic permeability of the material that is caused by the change of microstructure, the difference in stress and tissue distribution and obtained by the calculation with the effective field method.
3.5 static micromagnetic testing
The micromagnetic testing carried out when the magnetic moment in a magnet is in a state of equilibrium under the action of an external static magnetic field or an environmental magnetic field.
3.6 dynamic micromagnetic testing
The micromagnetic testing that is carried out when an external dynamic magnetic field exists and the magnetic moment in a magnet is in a time-varying state under the action of the effective field.
4 Method overview
4.1 Testing principle
Due to the changes in stress, structure, and microstructure in metal materials, under the action of external magnetization fields or environmental magnetic fields, the micromagnetic parameters of the material change, resulting in the generation of corresponding abnormal electromagnetic signals. Through the processing and analysis of abnormal signals, information such as stress distribution (magnitude and direction), material structural change (type, degree, and location), phase transition (quantity and distribution area), etc. can be obtained, which can be used for the evaluation of the mechanical property, high-and-low temperature performance and corrosion resistance of the materials.
According to whether the magnetic moment of the material changes with time during f) Detection of corrosion risk region of metastable stainless-steel material and evaluation of its corrosion performance, etc.
5 Requirements for personnel
The personnel who carry out the test according to this document should be qualified and certified according to the system agreed by the parties to the contract, and the employer or its agent shall conduct on-the-job training and operation authorization for the personnel.
6 General testing technological procedures
General testing technological procedures should be formulated in accordance with the requirements of this document. The general testing technological procedures shall include at least the following elements:
a) Scope of application;
b) The number of reference document;
c) Qualification of testing personnel;
d) Testing instruments and equipment, such as testing instruments, probes, magnetization devices (if any), and testing data acquisition and analysis software; e) Information on the tested objects, such as the geometrical shape and size, material, design and operating parameters, heat treatment information (optional), and relevant historical data;
f) Determination of testing method and sensitivity;
g) Determination of testing coverage and scanning area;
h) Surface condition of the tested objects;
i) Timing of testing;
j) Interpretation of the testing process and data analysis;
k) Evaluation of test results;
l) Testing records, reports, and data archiving;
m) Personnel for compiling, review and approval;
n) Date of compiling.
7 Testing equipment and instruments
7.1 Testing instruments
The testing instrument shall have functions such as data acquisition, digital signal conditioning and filtering, waveform display, analysis, and storage, and shall at least meet the following requirements:
a) Measure the magnetic/electromagnetic field intensity and its distribution on the surface of the tested object, and the sensitivity of the magnetic field measurement shall not be less than 0.5 mV/G;
b) The response time of dynamic electromagnetic field measurement shall not be more than 0.1 s;
c) Display the detection signal;
d) Offer the quantitative evaluation curve of the state of the tested object; e) Automatically store the testing results, and the original data corresponding to the detection signal waveform.
7.2 Probes
The structural form, applicable materials, temperature, and the performance parameters for magnetic/electromagnetic field measurement of the probe shall be provided. 7.3 Magnetizing apparatus
According to the requirements of the static/dynamic micromagnetic testing method, it is determined that the AC magnetization or DC magnetization is adopted for magnetizing apparatus; the intensity and direction of the magnetization field shall be adjustable according to the testing object.
7.4 Maintenance and calibration of testing equipment
Written procedures shall be developed, and the periodic maintenance of testing equipment shall be carried out to ensure equipment function; testing equipment shall be calibrated at least once a year.
The calibration object shall at least include the instrument host, probe, and magnetizing apparatus (if any). The host gain and bandwidth of the instrument host shall be calibrated; the sensitivity, accuracy, and response speed of the probe shall be calibrated with a standard magnetic field, and the uniformity and intensity of the magnetizing field of the magnetizing apparatus shall be calibrated.
structures on the surface of the inspection areas of the tested objects; the surface of the inspection areas of the tested objects shall not have magnetic shielding material, magnetic coating or cladding layer, and the maximum allowable thickness of nonmagnetic cladding layer shall be determined according to the testing method and the sensitivity of the testing instrument.
8.3 Testing modes
Static micromagnetic testing, dynamic micromagnetic testing, or the combined testing mode can be used.
8.4 Test records
The test records shall at least include the content specified in 10.2, and the test records and data shall be kept in accordance with the contract.
8.5 Static micromagnetic testing
The following steps shall be followed to implement static micromagnetic testing: a) Determine the surface state of the tested object, set the probe, and scan the coverage area;
b) Determine the intensity and direction of the environmental magnetic field, as well as the form, intensity, and direction of the external magnetic field (optional); c) Place the probe at a fixed measuring point of the tested object, and start the testing after the magnetization field is in a stable state and the change rate of the magnetic/electromagnetic field is not more than 1%;
d) Determine the scanning direction and sequence to ensure 100% coverage of the inspection area;
e) Record the complete magnetic/electromagnetic field on the surface of the tested object;
f) Determine the abnormal parts and signal distortion positions with uneven areas on the surface of the tested object, and mark them;
g) If necessary, scan and test the above-mentioned parts in the cross directions. 8.6 Dynamic micromagnetic testing
The following steps shall be followed to implement dynamic micromagnetic testing: a) Determine the surface state of the tested object, set the sensor, and scan the coverage area;
b) Determine the form, intensity, direction, and application area of the external magnetic field;
c) Determine the magnetization loading sequence and intensity, and place the probe on the surface of the tested object;
d) Determine the measuring position and scanning method to ensure 100% coverage of the inspection area;
e) Record the complete magnetic/electromagnetic field on the surface of the tested object;
f) Determine the abnormal parts and signal distortion positions with uneven areas on the surface of the tested object, and mark them;
g) If necessary, scan and test the above-mentioned parts in the cross directions. 8.7 Real-time analysis and processing of testing data
During the testing, the distribution, intensity, and sequential variation of the magnetic field shall be analyzed in real-time. For uniaxial stress measurement, the reliability and stability of the measurement data shall be verified; for non-uniformity detection, abnormal areas shall be identified.
9 Evaluation of test results
9.1 Stress measurement and evaluation of stress distribution
For the uniaxial stress measurement, the influencing factors such as the direction of the environmental magnetic field, expected stress direction and measurement environment, and the validity of parameters of the measured magnetic/electromagnetic field shall be first determined; then, carry out the conversion of the stress equivalent magnetic field according to the testing method and give the measurement result of the uniaxial stress. For the evaluation of stress distribution, the magnitude, direction, and nature of stress shall be converted according to the measured magnetic field parameters, and a stress distribution map shall be given. According to the stress distribution map, determine the uneven area of stress distribution or the stress distribution curve, the maximum/minimum value of stress, and the stress distribution unevenness. 9.2 Evaluation of uneven structure
For the evaluation of the structure, the equivalent magnetic permeability of the measured magnetic field parameters shall be used as the final parameter for evaluation, and it shall be compared with the relative magnetic permeability of conventional

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